In Japanese Patent Application Laid-Open No. 2010-233390 an inverter that drives a permanent-magnet synchronous motor is described, and a rotation position of the motor is detected based on a line voltage of the motor. In Japanese Patent Application Laid-Open No. 2010-233390, phase voltages are detected, and a line voltage is calculated based on these phase voltages. Then, by detecting a zero-crossing point of these line voltages, a rotation position of the motor is determined to a position corresponding to the zero-crossing point.
Further, as techniques relevant to the present disclosure, Japanese Patent Application Laid-Open No. 2011-19348 and Japanese Patent No. 2609840 are disclosed.